Fats and oils are compounds widely used in food. There is no chemical difference between a fat and an oil, the only distinction being that fats are solid at room temperature while oils are liquid. For simplicity, the term fat will be used throughout to include both fats and oils. Fats form one of the three classes of foods, the other two being carbohydrates and proteins. Fats contain more than double the number of calories per unit weight of carbohydrates or proteins. Furthermore, fats in the diet have become linked with a wide number of other undesirable effects on humans, ranging from heart disease to cancer. While these undesirable effects are now widely recognized, the taste, mouthfeel, and other organoleptic properties of fat in food are so desirable that it is not feasible to simply omit fat from food. Accordingly, it would be beneficial to reduce or eliminate the level of fat in food by replacing it with other materials which mimic fat's organoleptic and functional properties. A wide variety of fat replacements and substitutes have been taught for this purpose, including sucrose polyesters, pectin, carageenan, protein microparticulates, beta-glucans, and hemicelluloses. However, to date, starch derivatives of various types have shown the most promise in serving as acceptable fat replacements.
Starch is a plant material whose chemical composition is a polymer of thousands of anhydroglucose (C.sub.6 H.sub.10 O.sub.5) units. It is a member of the class of compounds known as polysaccharides in that it contains three or more saccharide units. It is also a member of the broader, carbohydrate class of compounds, which class includes monosaccharides, disaccharides, and polysaccharides. Starch molecules exist as essentially unbranched chains consisting predominantly of 1,4-linkages between the anhydroglucose units, known as amylose, and as branched chains consisting of both 1,4- and 1,6-linkages, known as amylopectin. The linear, short chain sections of the amylopectin molecule which are connected to the longer backbone are sometimes referred to as terminal amylose groups and generally are composed of about 10 to 50 anhydroglucose units.
Starch occurs naturally in plants in the form of granules having an average size of about 5 to 100 microns and containing thousands of individual starch molecules bound tightly together. Unmodified starch granules are insoluble in cold water, but can be dissolved by heating at a temperature of about 70.degree. to 90.degree. C. at atmospheric pressure, at which point the granules gradually swell and rupture and the individual molecules pass into solution. This process by which starch granules swell and rupture is alternatively referred to as gelatinization, pasting, or cooking.
The major commercial source of starch is corn (also known as maize), but potatoes, wheat, barley, rice, and tapioca are also important sources. The relative amounts of amylopectin (branched chains) and amylose (straight chains), as well as the average number of anhydroglucose units in a molecule (commonly known as the Degree of Polymerization, or D.P.) varies with the species of plant. For example, common dent corn starch contains about 72 percent amylopectin and 28 percent amylose; waxy maize corn starch contains nearly 100 percent amylopectin; and a common high amylose corn starch contains about 45 percent amylopectin and 55 percent amylose. Corn starch amylopectin has a D. P. of about 300,000 to 3,000,000 while amylose has a D. P. of about 800 to 8,000.
Corn starch is often modified chemically to alter its physical properties for a given application. One common modification is to substitute other chemical groups onto the hydroxyl groups of the starch molecules. The amount of substitution is expressed as the Degree of Substitution, or D.S. A starch molecule having one substituted group per anhydroglucose unit is defined as having a D.S. of one. A molecule having one substituent per 2 anhydroglucose units has a D.S. of 0.5., and so on. Another common modification is to treat the starch with an agent such as acid or enzyme to cleave some of the bonds between the anhydroglucose units and thereby reduce the average D. P. of the starch molecules. Starches having a reduced D. P. are said to be hydrolyzed or converted. They are often described in terms of their Dextrose Equivalent, or D. E., which is defined for an individual molecule as 100 / D. P. Accordingly, the monosaccharide dextrose, also known as glucose, has a D. P. of 1 and a D. E. of 100. Dextrose Equivalent is a convenient measure of the sweetness of a starch derivative and is widely used in the corn refining industry. In a mixture of molecules having different D.P.'s, D.E. can be viewed as a non-weighted average of the D.E.'s of the individual molecules. Depending upon the population distribution, two mixtures having the same average D.P. can have different D.E.'s, as shown by the following example.
Assume mixture A contains 6 starch derivative molecules, each one having a D.P. of 2 and a D.E. of 50. The average D.P. of the mixture is, of course, 2 (2+2+2+2+2+2/6) and the D.E. of the mixture is 50 (50+50+50+50+50+50/6). Now consider mixture B which also contains 6 molecules, but of the following distribution: The first molecule has a D.P. of 4 and a D.E. of 25; The second molecule has a D.P. of 3 and a D.E. of 33.33; The third molecule has a D.P. of 2 and a D.E. of 50; and the remaining three molecules each has a D.P. of 1 and a D.E. of 100. This mixture has an average D.P. of 2 (4+3+2+1+1+1/6), the same as mixture A. But mixture B has a D.E. of 68 (25+33.33+50+100+100+100/6).
As previously mentioned, a number of starch derivatives have been disclosed as fat replacements. One class of starch derivatives are those which are granular and converted in a non-alcohol process. Chiou et al., European Pat. Appln. No. 91-301368.6, published Aug. 28, 1991, which is incorporated by reference, discloses a granular starch hydrolysate prepared by heating starch in a strongly acidic, aqueous, non-alcohol slurry at a temperature below the gelatinization temperature. The resulting hydrolysate exhibits an unchanged ratio of 1,6- to 1,4- linkages, indicating that the conversion process cleaves the two types of linkages equally. The preferred starch hydrolysate has a D.E. of about 5.0 to 7.0 and an average molecular weight of about 4500 to 5000. These figures indicate that this hydrolysate contains a relatively high amount of low D.P. (&lt;20) molecules. This hydrolysate is sold as a fat replacement under the trademark STELLAR by the A. E. Staley Manufacturing Company. The method of preparation disclosed by Chiou et al. is related to the well known Lintnerization process.
A second class of starch derivatives are those which are granular, alcohol-processed, but not converted. Eastman et al., U.S. Pat. No. 4,465,702, issued Aug. 14, 1984, discloses a nonbirefringent, cold-water-swelling, granular starch material prepared by subjecting ungelatinized starch, in a slurry in selected aqueous alcohols, to conditions of high temperature and pressure. The process does not significantly affect the D.P. of the starch molecules. This starch material is a component of the ready-to-spread cake frosting disclosed in Augustine et al., U.S. Pat. No. 4,761,292, issued Aug. 2, 1988. Augustine et al. state that the starch is believed to play a role in imparting a desirable consistency to the frosting even at relatively low fat levels.
A third class of derivatives taught as fat replacements are pregelatinized (nongranular) starches. Furcsik et al., International Pat. Appln. No. PCT/US90/04013, published Feb. 7, 1991, discloses gelatinized starch derivatives having a D.E. of 5 to 15 derived from high amylose starch which exhibit relatively high gel strengths and can be used as fat replacements. Zallie et al., U.S. Pat. No. 4,937,091, issued Jun. 26, 1990, and Chiu, U.S. Pat. No. 4,971,723, issued Nov. 20, 1990, disclose pregelatinized starch derivatives which are used to lend fat-like textures to aqueous dispersions, such as replacements for caseinate in imitation cheese. The derivatives are debranched using an enzyme, such as Pullulanase, which cleaves the 1,6- linkages in amylopectin. The preferred derivatives comprise about 80% short chain amylose and 20% partially debranched amylopectin. The use of enzymes to reduce D.P. suffers from several disadvantages. First, the process is slow. Second, biological contamination is possible. And third, the enzyme cannot act on granular starch so the process works only with pregelatinized starch.
A fourth class of starch derivatives are dextrins. Lenchin et al., U.S. Pat. No. 4,510,166, issued Apr. 9, 1985, discloses the use of tapioca dextrins having a D.E. of less than about 1.5 as fat replacements in certain foods. These dextrins retain their granular structure, but contain molecules randomly shortened by the conversion process.
A fifth class of starch derivatives worthy of mention are those which are aqueous-alcohol processed, even though they are not disclosed as fat replacements. Battists, U.S. Pat. No. 3,351,489, issued Nov. 7, 1965, discloses stable amylose dispersions prepared by heating amylose starch in boiling acidic liquid mediums containing water or other liquids such as sugar solutions, polyols, and alcohols. Exposure to these conditions gelatinizes the starch. Battista teaches that these dispersions are useful as bases for cosmetics and pharmaceutical preparations, foods, and packaging films, but does not mention their use as fat replacements. A process for producing granular dextrins is disclosed in Sugimoto, U.S. Pat. No. 3,799,805, issued Mar. 26, 1974, which is incorporated by reference. The dextrins are prepared by heating granular starch with acid in an aqueous solution of an organic solvent such as propanol, ethanol, methanol, acetone, and fatty acids. Sugimoto teaches that the resulting dextrins are useful in the production of maltodextrins, but contains no suggestion regarding their use as fat replacements. Another type of aqueous alcohol-treated starch is disclosed in Eastman, U.S. Pat. No. 4,837,314, issued Jun. 6, 1989. These starches are highly derivatized prior to alcohol treatment and are used as replacements for gum arabic.
Despite all the attempts to provide a versatile fat replacement from starch, none has heretofore been discovered and the search continues throughout the food industry.